The H1N1 flu pandemic is one of the major infectious threat of the past half century. it is rapidly progressing worldwide and a substantial number of patients get severe H1N1 related pneumonia that requires mechanical ventilation and admission to the intensive care unit. The acute respiratory distress syndrome is associated with a substantial mortality and morbidity partly as a consequence of uncontrolled lung and systemic inflammation. many physicians are trying to counteract this pro-inflammatory storm by the use of corticosteroids albeit these drugs may cause super infection or metabolic disorders. Thus, there is a need for a randomized double blind, placebo controlled trial to define the benefit to risk ratio of corticosteroids in this patient.